Multi-stage friction vacuum pump

ABSTRACT

A multi-stage vacuum pump includes at least one turbo-compressor stage ( 11 ) and is equipped with a circular compressor stage ( 33 ) on the pressure side of the turbo-compressor stage. The pump has small axial dimensions, enabling the compression to be increased without significantly increasing the space requirement.

BACKGROUND

The invention refers to a multi-stage friction vacuum pump with at leastone axially compressing turbo-compressor stage having a rotor rotatingabout its axis and comprising rotor discs projecting between stationarystator discs.

Turbomolecular pumps belong in the group of friction vacuum pumps withwhich a high vacuum can be created, for example for recipients used insemi-conductor manufacturing or for mass spectrometers. A multi-stagefriction vacuum pump described in U.S. Pat. No. 7,011,491 comprises oneor a plurality of turbo-compressor stages each formed by a rotor withradially projecting rotor discs and a stator with radially projectingstator discs. The rotor discs and the stator discs mesh in a comb-likemanner with little space between them. They cause a molecular flow axialto the rotor axis. In addition to the turbo-compressor stage, a circularcompressor stage may be provided which comprises a rotor with axiallyprojecting rotor blades arranged on a circular line and a stator withaxially protruding stator blades arranged on a circular line. The rotorblades and the stator blades mesh alternately and cause a molecular flowthat is directed either radially inward or radially outward, dependingon the sense of rotation and the angle of attack of the blades.

It is the object of the invention to provide a multi-stage frictionvacuum pump with at least one turbo-compressor stage, wherein the stagesare arranged in series in the flow path and which is to yield highercompression.

SUMMARY

The vacuum pump comprises a turbo-compressor stage and a circularcompressor stage arranged downstream in the flow path. Whereas theturbo-compressor stage is suited to generate a high vacuum, thedownstream circular compressor stage serves to effect a pressureincrease. As a consequence, since the gas volume is reduced bycompression, the circular compressor stage can have small dimensions.The circular compressor stage has a small axial dimension since it isflown through mainly in the radial direction. The overall dimensions ofthe friction pump are not significantly increased by the circularcompressor stage, but the compression is clearly intensified withrespect to single-stage friction vacuum pumps. The present combinationof an upstream turbo-compressor stage and a downstream circularcompressor stage offers the advantage of requiring little space whilehaving a high compression capacity.

According to a preferred embodiment of the invention, theturbo-compressor stage and the circular compressor stage are integratedin a common combination of rotor and stator. This means that the rotorsof both compressor stages are formed by a single combined rotor and thestators of both compressor stages are also formed by a single combinedstator. Thus, the dimensions and the weight can be reduced further.

The present friction vacuum pump is preferably designed as a multipleinlet pump. It comprises at least two axially spaced, seriallycompressing turbo-compressor stages between which an intermediate inletis located. A circular compressor stage is arranged on the compressorside of the first turbo-compressor stage and/or the secondturbo-compressor stage. Such a pump is particularly suited for use inthe context of mass spectrometers. Due to the increased gas flow at theintermediate inlet to which the analyzing means of the mass spectrometeris connected, the gas flow at the intermediate inlet is increasedwithout a negative effect on the pressure at the high vacuum inlet. Theincrease in the gas flow at the intermediate inlet means an increasedsensitivity of the mass spectrometer.

Depending on the compression ratio, different types and structures maybe used for the circular compressor stages, such as described in U.S.Pat. No. 7,011,491.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a detailed description of embodiments of the inventionwith reference to the drawings. These embodiments should not be seen aslimiting the scope of protection of the present invention. Rather, thisscope is defined by the claims and the equivalents thereof.

In the Figures:

FIG. 1 illustrates a longitudinal section through a friction vacuum pumpof the present invention,

FIG. 2 is an illustration of the circular compressor stage,

FIGS. 3 and 4 are longitudinal sections through different embodiments ofcircular compressor stages.

DETAILED DESCRIPTION

The friction vacuum pump illustrated in FIG. 1 comprises a housing 10 ofsubstantially cylindrical design, which has a high vacuum port HV at oneend. In the housing wall an intermediate inlet ZE1 is provided that isopen to the side. The intermediate inlet ZE1 is bridged by webs 18 thatconnect the stator parts with each other.

In the front portion 10 a of the housing 10, a first turbo-compressorstage 11 formed by a stator 12 and a rotor 13 is arranged. The stator 12has a plurality of stator discs 15 directed radially inward from acircumferential wall 14. The rotor 13 has a plurality of rotor discs 16projecting radially outward between the stator discs 15. A drive 17including a fast rotating electric motor drives the rotor 13 at a numberof rotations between 30,000 and 60,000 rpm.

A second turbo-compressor stage 21 is arranged on the compressor side ofthe first turbo-compressor stage 11 and has its inlet connected with theintermediate inlet ZE1. The turbo-compressor stage 21 is formed by astator 22 and a rotor 23. The stator 22 comprises a plurality of statordiscs 25 directed radially inward from a circumferential wall 22. Therotor 23 comprises a plurality of rotor discs 26 projecting radiallyoutward between the stator discs 25. The rotors 13 and 23 are fixedlyinterconnected and are driven together by the drive 17.

In the housing 10, a further compressor stage 30 follows the secondturbo-compressor stage 21, this further compressor stage beingadditionally connected with an intermediate inlet ZE2. For example, thecompressor stage 30 is a Holweck stage or another molecular pump, forexample a Gaede pump, a Siegbahn pump, an Englander pump or a sidechannel pump.

In the present embodiment, a circular compressor stage 33 is providedfollowing the first turbo-compressor stage 11. It comprises a rotor disc34 which is a part of the rotor 13 of the turbo-compressor stage 11, anda stator disc 32 which is a part of the stator 12. The rotor disc 34comprises rotor blades 35 arranged on concentric circles, and the statordisc 32 comprises stator blades 36 also arranged on concentric circlesand engaging in gaps between the rotor circles, as is illustrated inFIG. 2. The stator blades and the rotor blades are inclined oppositelywith respect to the radial direction. Depending on the sense of rotationof the rotor, the circular compressor stage 33 conveys either radiallyoutward or radially inward. In the present embodiment, the conveyingdirection is indicated by the arrow 37. The gas transport passes fromthe high vacuum inlet HV through the turbo-compressor stage 11 andradially inward from the circumference thereof through the circularcompressor stage 33 and from there through a gap 38 to the intermediateinlet ZE1. From the intermediate inlet ZE1, the turbo-compressor stage21 conveys the gas to the compressor stage 30. The second intermediateinlet ZE2 also opens into the compressor stage 30. The compressor stage30 conveys to an outlet (not illustrated).

One of the rotor discs 16 of the turbo compressor stage 11 is thesupporting disc for the rotor blades of the circular compressor stage33. The stator disc of the circular compressor disc simultaneously formsthe end wall of the pressure-side end of the turbo-compressor stage 11.

It is a special advantage that the circular compressor stage 33 is quasiintegrated in the turbo-compressor stage 11. The only additional effortrequired are the rotor and stator blades 35, 36 additionally provided atthe rotor and the stator of the turbo compressor stage.

As an alternative to the present embodiment, a circular compressor stage33 may also be provided behind the second turbo-compressor stage 21. Thecircular compressor stage arranged on the pressure side of therespective turbo-compressor stage and integrated in the turbo-compressorstage increases the gas flow on the pressure side. For a massspectrometer connected thereto, this means an increase in sensitivity.

FIG. 3 illustrates the gas flow 40 through the circular compressor stage33 flowing radially from the outside inward.

In the embodiment of FIG. 4, the blade surface of the rotor disc 34 isconical. The rotor blades 35 have an axial length that decreases as theradius of the circular path decreases.

It is also possible to use a circular compressor stage with a pluralityof discs and alternately outward and inward directed flow paths, as isgenerally illustrated in FIG. 7 of U.S. Pat. No. 7,011,491.

The invention has been described with reference to the preferredembodiments. Modifications and alterations may occur to others uponreading and understanding the preceding detailed description. It isintended that the invention be constructed as including all suchmodifications and alterations insofar as they come within the scope ofthe appended claims or the equivalents thereof.

1. A multi-stage friction vacuum pump comprising: at least one axiallycompressing turbo-compressor stage with a rotor rotating about its axisand having rotor discs projecting between stationary stator discs; aradially compressing circular compressor stage arranged on thecompressor side of the turbo-compressor stage, said circular compressorstage comprising a rotor having axially projecting rotor blades arrangedon circular paths and a stator having axially projecting stator bladesarranged on circular paths, the stator blades engaging in radial gapsbetween adjacent circular paths of rotor blades.
 2. The friction vacuumpump of claim 1, wherein the rotor blades of the circular compressorstage are arranged on a rotor body of the turbo-compressor stagecarrying the rotor discs.
 3. The friction vacuum pump of claim 1,wherein the stator blades are arranged on a stator body of theturbo-compressor stage carrying the stator discs.
 4. The friction vacuumpump of claim 1, as a multi-inlet pump, further including: at least twoaxially spaced, serially compressing turbo-compressor stages betweenwhich an intermediate inlet is situated, and a circular compressor stageon the compressor side of the first turbo-compressor stage.
 5. Thefriction vacuum pump of claim 1, as a multi-inlet pump, furtherincluding: at least two axially spaced, serially compressingturbo-compressor stages between which an intermediate inlet is situated,and a circular compressor stage on the compressor side of the secondturbo-compressor stage.
 6. The friction vacuum pump of claim 1, whereinthe circular compressor stage compresses radially inward.
 7. Thefriction vacuum pump of claim 1, wherein in that the circular compressorstage is designed with at least two stages and alternately compressesone of radially inward and radially outward.
 8. The friction vacuum pumpof claim 1, wherein the rotor blades have an axial length that tapers ina direction of compression.